1. Field of the Invention
The present invention relates to an electron emission device, and in particular, to an electron emission device which has an electrode structure for preventing the electrostatic charges from being accumulated on the insulating layer.
2. Description of Related Art
Generally, electron emission devices are classified into a first type where a hot cathode is used as an electron emission source, and a second type where a cold cathode is used as the electron emission source. The cold cathode electron emission devices, in turn, include field emitter array (FEA) devices, surface conduction emitter (SCE) devices, metal-insulator-metal (MIM) devices, metal-insulator-semiconductor (MIS) devices, and ballistic electron surface emitter (BSE) devices.
Electron emission devices may have different structures depending on their specific type. However, most types include two substrates separated by some form of a spacer and forming a vacuum chamber in the space between the two substrates. An electron emission structure with driving electrodes is formed at one of the substrates to emit electrons. Phosphor layers and an electron accelerating electrode are formed on the other substrate to emit light and display the desired images. The driving electrodes are usually formed with two electrodes placed perpendicular to each other.
The rate of electron emission is controlled through operating the driving electrodes by the well-known matrix address technique. An insulating layer is formed between the first and the second electrodes to electrically insulate the two from each other. The substrate with the electron emission structure, and the substrate with the phosphor layers are usually parallel to each other with a distance in between. A sealing material, such as a frit, is used to seal the substrates to each other to form the vacuum chamber. The vacuum chamber, thus formed, is partitioned into a display area and a non-display area.
In electron emission devices with the above conventional structures, the insulating layer in the display area is usually covered with one or two electrodes. On the other hand, the insulating layer in the non-display area around the frit-coated sealing line is not covered by electrodes while being exposed to the vacuum inside the chamber. As a result of this structure, static charges are accumulated on the insulating layer of conventional electron emission devices in the non display areas and cause device failures such as abnormal operation, arcing, and flashover.
In order to prevent these problems, U.S. Pat. No. 5,929,560 discloses a field emission display device where an ion shield layer is formed on the insulating layer in the non-display area to prevent the accumulation of static charges on the insulating layer. The ion shield layer is electrode layer supplied with a voltage independently from the electrodes placed at the display area, and prevents static charges from accumulating on the insulating layer in the non-display area.
In conventional techniques, including the ion shield technique explained above, because the ion shield layer receives its driving voltage from an IC separate from the IC used for driving the emission electrode, the number of structural components and therefore the cost of production, are increased.